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Thread: Need help interpretting the schematic for an EMG PA2 boost circuit

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    Super Toneologist Jack_TriPpEr's Avatar
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    Default Need help interpretting the schematic for an EMG PA2 boost circuit

    The product page on the EMG site for the PA2 boost circuit ( https://www.emgpickups.com/pa2.html) has a downloadable wiring instruction sheet. Within that sheet, is a schematic for the circuit of the PA2 - see attached pic. Can anyone tell me what the two triangle symbols with the plus sign inside them represent? I have not found a reference online for that exact symbol. I have found descriptions for triangle symbols that are slightly different - none exactly like these two.

    Edit: I suspect they represent the boost itself, but then that makes me confused about the circuit, because you are supposed to be able to turn the boost on or off. Yet this seems to show the input signal going through the boost in either case (?)

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    Last edited by Jack_TriPpEr; 06-01-2020 at 02:58 PM.
    Quote Originally Posted by GuitarDoc View Post
    Good diagram Shadowfire90, but it isn't what the OP wants.
    Quote Originally Posted by Sanford View Post
    The hardest part about tone chasing is losing the expectations associated with the hardware.
    Quote Originally Posted by blueman335 View Post
    I've been slammed here a few times myself for not going with the crowd. I'd rather go in a different direction, and know why, then follow everyone else and not know why.

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    of the Forum PFDarkside's Avatar
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    Default Re: Need help interpretting the schematic for an EMG PA2 boost circuit

    Im assuming a very simple inverting OpAmp schematic, omitting a decent amount. The bottom one being a unity gain amplifier and the top one having variable gain set by the pot.
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    LoveMachineologist jeremy's Avatar
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    Default Re: Need help interpretting the schematic for an EMG PA2 boost circuit

    thats a block diagram, not a schematic and i suspect darkside is correct that one is just a unity gain amp while the other is a boost

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    Super Toneologist Jack_TriPpEr's Avatar
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    Default Re: Need help interpretting the schematic for an EMG PA2 boost circuit

    Quote Originally Posted by PFDarkside View Post
    I’m assuming a very simple inverting OpAmp schematic, omitting a decent amount. The bottom one being a unity gain amplifier and the top one having variable gain set by the pot.
    Ah, the 2nd amp being unity gain - that makes sense. Thanks!
    Quote Originally Posted by GuitarDoc View Post
    Good diagram Shadowfire90, but it isn't what the OP wants.
    Quote Originally Posted by Sanford View Post
    The hardest part about tone chasing is losing the expectations associated with the hardware.
    Quote Originally Posted by blueman335 View Post
    I've been slammed here a few times myself for not going with the crowd. I'd rather go in a different direction, and know why, then follow everyone else and not know why.

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    Super Toneologist Jack_TriPpEr's Avatar
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    Default Re: Need help interpretting the schematic for an EMG PA2 boost circuit

    Quote Originally Posted by jeremy View Post
    thats a block diagram, not a schematic and i suspect darkside is correct that one is just a unity gain amp while the other is a boost
    Ahh, thanks for the clueing me in that not everything that looks like a schematic, is actually a schematic. And for corroborating Darkside's theory.
    Quote Originally Posted by GuitarDoc View Post
    Good diagram Shadowfire90, but it isn't what the OP wants.
    Quote Originally Posted by Sanford View Post
    The hardest part about tone chasing is losing the expectations associated with the hardware.
    Quote Originally Posted by blueman335 View Post
    I've been slammed here a few times myself for not going with the crowd. I'd rather go in a different direction, and know why, then follow everyone else and not know why.

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    Slutbucker Pimpologist ArtieToo's Avatar
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    Default Re: Need help interpretting the schematic for an EMG PA2 boost circuit

    Quote Originally Posted by PFDarkside View Post
    I’m assuming a very simple inverting OpAmp schematic, omitting a decent amount. The bottom one being a unity gain amplifier and the top one having variable gain set by the pot.
    Yup. Can't add to that. Although, without +/- input labels, there's no way to know if its inverting, without watching the output on a scope.

    Edit: I take that back. You could temporarily connect the booster to just one pup. If it went OOP after activation with another pup, it would be inverting. If not, then it isn't inverting.
    Last edited by ArtieToo; 06-01-2020 at 03:22 PM.

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    LoveMachineologist jeremy's Avatar
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    Default Re: Need help interpretting the schematic for an EMG PA2 boost circuit

    ive used it only on one pup and it wasnt inverting

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    of the Forum PFDarkside's Avatar
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    Default Re: Need help interpretting the schematic for an EMG PA2 boost circuit

    Yeah, I was thinking inverting due to the layout and how there were two amplifiers it is being switched between (to keep phase the same whether engaged or not). Non-inverting makes more sense so you could use it on a single pickup and not cause additional phase issues.

    It’s an interesting layout though, rather than simply bypassing the boost entirely or switching from fixed unity resistor to potentiometer.
    Oh no.....


    Oh Yeah!

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    Super Toneologist Jack_TriPpEr's Avatar
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    Default Re: Need help interpretting the schematic for an EMG PA2 boost circuit

    Quote Originally Posted by jeremy View Post
    ive used it only on one pup and it wasnt inverting
    Quote Originally Posted by PFDarkside View Post
    Yeah, I was thinking inverting due to the layout and how there were two amplifiers it is being switched between (to keep phase the same whether engaged or not). Non-inverting makes more sense so you could use it on a single pickup and not cause additional phase issues.

    It’s an interesting layout though, rather than simply bypassing the boost entirely or switching from fixed unity resistor to potentiometer.
    Great insights, thanks again to you both
    Quote Originally Posted by GuitarDoc View Post
    Good diagram Shadowfire90, but it isn't what the OP wants.
    Quote Originally Posted by Sanford View Post
    The hardest part about tone chasing is losing the expectations associated with the hardware.
    Quote Originally Posted by blueman335 View Post
    I've been slammed here a few times myself for not going with the crowd. I'd rather go in a different direction, and know why, then follow everyone else and not know why.

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